The present invention relates to steering devices such as may be used with catheters, cannulae, guidewires and the like. More particularly, the present invention relates to catheters and guidewires that are steerable through body lumena or cavities, and are positioned within or aimed at obstructions, organs, or tissue within the body from a position external to the body.
Medical catheters generally comprise elongate tube-like members which may be inserted into the body, either percutaneously or via a body orifice, for any of a wide variety of diagnostic and interventional purposes. Such medical applications frequently require use of a catheter having the ability to negotiate twists and turns; this is particularly the case with regard to certain cardiovascular applications.
For such applications, the object is to reach and deliver some treatment or instrument to a remote lesion. Often, it is required that the instrument cross the lesion, which may consist of hard and inflexible tissue with a very rough surface, or even protruding flaps.
One such application, Percutaneous Transluminal Coronary Angioplasty (balloon angioplasty), requires manipulation of a catheter from a position outside the patient's body through extended portions of the patient's arterial system to the stenotic site for the purposes of alleviating the lesion by inflating a balloon. This particular procedure, performed with increasing frequency over the past years, is done in preference to open heart bypass surgery, when possible.
In a typical angioplasty procedure, a guidewire is transluminally inserted into the brachial or the femoral artery, to be positioned within the stenotic region and followed by a balloon catheter. The cardiologist usually pre-bends the distal tip of the guidewire before insertion and then rotates (or torques) the wire once it has reached a branch artery to enable the tip of the guidewire to enter the branch. If the angle of the bend needs to be adjusted, the guidewire is removed, re-bent and reinserted, sometimes several times during one angioplasty procedure. Particular difficulty is encountered with pre-bending in cases when an artery branches at one angle, and then sub-branches at a different angle. With repeated removal and reinsertion of the guidewire, the procedure is attended by the risk of significant trauma to the arterial lining, and in many cases, the obstruction cannot be reached at all with the guidewire and catheter.
Coronary arteries are tortuous and have many sub-branches. Often the obstruction is either located where the diameter of the artery is small or, by its very presence, the obstruction leaves only a very small opening through which a guidewire and/or catheter can be passed. Consequently the cardiologist often finds it very difficult to maneuver the guidewire or catheter, which is typically several feet long, from the proximal end.
In another application, Transluminal Laser Catheter Angioplasty (laser angioplasty), the delivery of laser energy from an external source to an intraluminal site to remove plaque or thrombus obstructions in vessels is accomplished by providing a waveguide such as a fiber optic bundle within a catheter. The nature of laser angioplasty requires even greater precision in control of the catheter, to position and aim the laser light at the specific plaques or thrombi to be removed.
These applications could all benefit from an increased degree of steerability of the tip of the guidewire or catheter from a remote site located external to the body. A variety of constructions have been proposed in the past to provide catheters which are steerable from the proximal end to enable the catheter to be aimed or advanced through non-linear cavities without removal for adjustments. Such constructions include those shown in U.S. Pat. No. 4,723,936 of Buchbinder; U.S. Pat. No. 4,921,482 of Hammerslag; U.S. Pat. No. 3,470,876 of Barchilon; U.S. Pat. No. 4,601,705 of McCoy, and others. These constructions involve shape memory alloy elements which may be heated to change their orientation, or devices employing wires or pulleys to steer the tip of a device from a handle located outside the body. However, each of these constructions has limitations.
Shape memory alloy devices have slow response due to reliance on heat transfer as the operative control mechanism. Also, shape memory devices in their superelastic state have a great deal of hysteresis, making them difficult to use for controlling position precisely. Devices making use of wires and or pullies for differential operation have problems achieving precise control over long distances, because long small diameter wires, requiring only minimal changes in length to actuate, do not afford very precise control. In addition, the cable tension required for such devices to work effectively dictates that the stiffness of the tip, which is critical to device effectiveness, is altered by the actuating mechanism. Also, the overall size of the device trades off against the ability to tension the cable, where the strain in the tensioned cable increases as device size decreases. It would therefore be desirable to achieve a remotely steerable catheterization device that does not incur penalties of stiffness, precision or size.